Drug Interactions between dabrafenib and efavirenz / lamivudine / tenofovir disoproxil

MONITOR: Coadministration of efavirenz with other agents known to induce hepatotoxicity may potentiate the risk of liver injury. Efavirenz has been associated with hepatotoxicity during postmarketing use. Among reported cases of hepatic failure, a few occurred in patients with no preexisting hepatic disease or other identifiable risk factors.

MANAGEMENT: The risk of hepatic injury should be considered when efavirenz is used in combination with other agents that are potentially hepatotoxic (e.g., acetaminophen; alcohol; androgens and anabolic steroids; antituberculous agents; azole antifungal agents; ACE inhibitors; cyclosporine (high dosages); disulfiram; endothelin receptor antagonists; interferons; ketolide and macrolide antibiotics; kinase inhibitors; minocycline; nonsteroidal anti-inflammatory agents; other HIV reverse transcriptase inhibitors; proteasome inhibitors; retinoids; sulfonamides; tamoxifen; thiazolidinediones; tolvaptan; vincristine; zileuton; anticonvulsants such as carbamazepine, hydantoins, felbamate, and valproic acid; lipid-lowering medications such as fenofibrate, lomitapide, mipomersen, niacin, and statins; herbals and nutritional supplements such as black cohosh, chaparral, comfrey, DHEA, kava, pennyroyal oil, and red yeast rice). Patients should be advised to seek medical attention if they experience potential signs and symptoms of hepatotoxicity such as fever, rash, itching, anorexia, nausea, vomiting, fatigue, malaise, right upper quadrant pain, dark urine, pale stools, and jaundice. Monitoring of liver function tests should occur before and during treatment, especially in patients with underlying hepatic disease (including hepatitis B or C coinfection) or marked transaminase elevations. The benefit of continued therapy with efavirenz should be considered against the unknown risks of significant liver toxicity in patients who develop persistent elevations of serum transaminases greater than five times the upper limit of normal.

MONITOR: Coadministration of efavirenz with other agents known to induce hepatotoxicity may potentiate the risk of liver injury. Efavirenz has been associated with hepatotoxicity during postmarketing use. Among reported cases of hepatic failure, a few occurred in patients with no preexisting hepatic disease or other identifiable risk factors.

MANAGEMENT: The risk of hepatic injury should be considered when efavirenz is used in combination with other agents that are potentially hepatotoxic (e.g., acetaminophen; alcohol; androgens and anabolic steroids; antituberculous agents; azole antifungal agents; ACE inhibitors; cyclosporine (high dosages); disulfiram; endothelin receptor antagonists; interferons; ketolide and macrolide antibiotics; kinase inhibitors; minocycline; nonsteroidal anti-inflammatory agents; other HIV reverse transcriptase inhibitors; proteasome inhibitors; retinoids; sulfonamides; tamoxifen; thiazolidinediones; tolvaptan; vincristine; zileuton; anticonvulsants such as carbamazepine, hydantoins, felbamate, and valproic acid; lipid-lowering medications such as fenofibrate, lomitapide, mipomersen, niacin, and statins; herbals and nutritional supplements such as black cohosh, chaparral, comfrey, DHEA, kava, pennyroyal oil, and red yeast rice). Patients should be advised to seek medical attention if they experience potential signs and symptoms of hepatotoxicity such as fever, rash, itching, anorexia, nausea, vomiting, fatigue, malaise, right upper quadrant pain, dark urine, pale stools, and jaundice. Monitoring of liver function tests should occur before and during treatment, especially in patients with underlying hepatic disease (including hepatitis B or C coinfection) or marked transaminase elevations. The benefit of continued therapy with efavirenz should be considered against the unknown risks of significant liver toxicity in patients who develop persistent elevations of serum transaminases greater than five times the upper limit of normal.

MONITOR: Coadministration with dabrafenib may decrease the plasma concentrations of drugs that are primarily metabolized by CYP450 3A4 and/or 2C9. Dabrafenib has been found in vitro to be an inducer of these isoenzymes. Onset of induction is likely to occur after 3 days of repeat dosing with dabrafenib; however, transient inhibition of CYP450 isoenzymes may be observed during the first few days of treatment. In 12 study subjects, administration of the CYP450 3A4 probe substrate midazolam following repeat doses of dabrafenib 150 mg twice daily for 15 days reduced midazolam peak plasma concentration (Cmax) by 61% and systemic exposure (AUC) by 74%. When a single 15 mg dose of warfarin was coadministered similarly with dabrafenib, the AUC of S(-) warfarin decreased by 37% and that of R(+) decreased by 33%. S(-) warfarin, the biologically more active enantiomer, is primarily metabolized by CYP450 2C9, while R(+) warfarin is a substrate of CYP450 3A4 and 1A2.

MANAGEMENT: Caution is advised when dabrafenib is prescribed with drugs that undergo metabolism by CYP450 3A4 and/or 2C9. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever dabrafenib is added to or withdrawn from therapy. Significantly reduced plasma concentrations and loss of efficacy may occur with sensitive substrates of CYP450 3A4 or 2C9 such as hormonal contraceptives, immunosuppressants (cyclosporine, everolimus, sirolimus, tacrolimus), ivacaftor, and warfarin-type anticoagulants. Alternatives to these medications should be considered if possible.